fix: recover from SSR errors in dev without a manual refresh

[birkskyum]

• Fixes [Bug?]: syntax errors in ./app.tsx causes uncaught 500 error #1648.

Problem

A syntax error in app.tsx leaves a 500 page that never recovers: fixing the file does nothing until you refresh by hand.

The ErrorOverlay branch in dev-server.ts looks like it covers this, but it is unreachable in a standard v2 app. configureServer bails out early when the server environment has dispatchFetch, and Nitro implements exactly that, so Nitro renders its own error page with no /@vite/client on it. None of that page's modules are registered for HMR, so the update that fixes the file is dropped, and Vite's client only self-reloads when the page has a vite-error-overlay mounted or receives a full-reload.

Fix

A dev middleware buffers HTML 5xx responses and appends a script that connects them to the HMR channel and reloads once the server renders again. Anything that is not an HTML 5xx passes through untouched, as do pages that already talk to the HMR client.

Two details worth calling out:

• Status and content type arrive as writeHead arguments rather than on res, and Nitro passes headers as a flat [name, value, ...] array. Reading only res.statusCode never detects the error, and leaving content-length in the array form truncates the body.
• Reloading on the HMR update alone is racy: Vite broadcasts it before the server environment picks the change up, so the reload re-renders the same 500. The script polls with backoff until the server returns non-5xx. Polling only starts on an HMR event, so an idle error page does not spam the terminal with error traces.

Testing

15 unit tests over injection, both writeHead header forms, and the middleware's buffering and pass-through paths. Verified the reporter's repro in Chromium: break app.tsx, fix it, page recovers on its own in ~0.5s. Units, typecheck, both e2e suites, and format:check pass.

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Latest commit: cea0314

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@solidjs/start	Patch

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